The proposal describes a 5 year mentored training experience designed to lead to an independent career in academic medicine. The applicant holds both MD and PhD degrees with research experience in molecular biology, biochemistry and cell biology; she is currently completing a clinical genetics fellowship. The environment at Baylor College of Medicine provides a unique combination of strengths in a variety of aspects of medical genetics (clinical care, diagnostic labs, and research) as well as basic science research. The laboratory mentor is a world renowned leader in the field of urea cycle disorders (UCD) and the members of the advisory committee have been carefully selected to provide expertise in several aspects of the proposed research project as well as provide career guidance for the physician-scientist applicant. The project combines mouse genetics, metabolic flux studies, and human clinical research to dissect the contribution of endogenous, urea cycle-derived Arginine flux to Nitric Oxide (NO) production. We will study Arginine and NO production in health and in specific diseases where NO has a proven role in the pathogenesis using both mouse models and human patients. The specific aims of this project include generating and characterizing a novel conditional knockout mouse model in which endogenous, intracellular Arginine production by the kidney is impaired. The results will be compared to human patients presenting with hyperargininemia and Arginine deficiency. Urea cycle disorders are enzymatic deficiencies that can provide insight into how Arginine availability may affect whole body NO production. By understanding this, we may be able to rationally devise pharmacological treatment for NO dysregulation in diseases such as diabetes, renal failure, and cardiovascular disease. While many of these therapeutic approaches remain speculative, better understanding of the underlying mechanisms that regulate the function will ultimately improve our ability to implement such therapies. This proposal will provide the applicant with training in new technologies in both human and mouse genetics, and dynamic stable isotope measurements. This period of mentored training in scientific design, implementation and communication will complement the applicant's continued development as a clinician, eventually resulting in an independent research program and a long-term career in academic medicine.